Pathology Harness: Evidence-Guided Diagnostic Finalization for Pathology Agents

Recent advances in computational pathology have enabled systems that combine whole-slide image analysis with diagnostic reasoning. These systems aggregate regional features, generate morphological descriptions, or navigate tissue at multiple magnifications to formulate diagnostic proposals. However, producing a plausible proposal does not ensure that the collected observations document the morphological findings and differential checks needed to support it. This gap raises a practical question: when is the available evidence sufficient to finalize a diagnosis, and what should be examined when it is not? To address this problem, we introduce Pathology Harness, a framework that governs diagnostic finalization through explicit evidence requirements. The framework binds each fixed diagnostic proposal to an evidence contract, audits the recorded observations against its requirements, and determines whether to release the proposal, request further observation, or block finalization. To resolve recoverable evidence gaps, we develop Differential-Contract Evidence Acquisition (DCE-Scout), which selects complementary regions and magnifications under a limited observation budget. Newly acquired findings can support or contradict the proposal and are recorded for renewed audit, preserving the basis for each release decision. Experiments reveal that even correct diagnostic proposals can lack the recorded evidence required for finalization, highlighting a gap between diagnostic prediction and evidential support. Pathology Harness addresses this gap through targeted evidence acquisition and selective release, allowing more cases to meet explicit finalization criteria than initial-record auditing alone and lowering the error rate among released diagnoses compared with unconditional release. These findings demonstrate the value of coupling evidence acquisition with explicit finalization criteria and suggest a promising direction for pathology agents that produce traceable, evidence-supported diagnostic outputs.